Green’s Dictionary of Slang

1. to talk nonsense, to lie; thus trash-talking n. and adj.

[1869		Brooklyn Daily Eagle 29 Oct. 2: If we began to excuse and scrutinise the trash that is talked in political meetings, with a view to exclude all the statements we deem filthy and false, we should be responsible for the good faith of the speakers and the truth of the statements which we did report.].
2002		‘Touré’ Portable Promised Land (ms.) 115: Trash-talkin. Special citation: Muhammad Ali.
2007		J. Stahl ‘Pure’ in Love Without 169: I’m not thinking about my trash-talking backside.

2. to talk insultingly, disparagingly; thus trash talking n.

1974		N.Y. Times 12 May n.p.: [...] be it bad walking, trash talking or throwing a baseball.
1997		Simon & Burns Corner (1998) 249: A homicide detective is left standing over the corpse, trash talking with his partner about the stupidiy of the victim.
2000		J. Ellroy ‘Balls to the Wall’ in Destination: Morgue! (2004) 6: Paret trash-talked Griffith. Paret called him queer.
2006		G. Iles Turning Angel 128: So would the fathers who are trash-talking Dr. Elliott.
2012		D. Spivey ‘If You Were Only White’ 41: Paige [...] admired [Jack Johnson’s] boasting, trash talking to opponents, and superiority in the ring.